Population ecology of small rodents in sown wild flower areas in western Switzerland

Summary. — Small mammal communities on four sown wild flower areas in western Switzerland were studied from spring to autumn 2005 using the capture-recapture method. We trapped 666 animals belonging to Microtus arvalis, Apodemus sylvaticus, Apodemus flavicollis and Crocidura russula. M. arvalis, the most abundant species, reached a peak of 581 animals/ ha known to be alive (MNA ) on one area in late September. Spring populations of M. arvalis were very low on all fields. A preliminary study in 2003-2004 showed a very low number of animals known to be alive during the winter months and a similar population growth in spring. Population turnover was generally high with up to 81 % of the population renewed in a one-week period (August). On all fields, there was a surplus of female M. arvalis. In August and September, the difference from 1 : 1 ratio was significant in one field, apparently a result of differential survival rate and recruitment between sexes. There was no significant difference in body mass between adult females and adult males. The second most frequent species, A. sylvaticus reached densities of up to 225 animals/ ha on one area, but only 60-100 animals/ ha, on the other three sites.